Has anyone tried removing either of these products from the top deck of their boat? I really want to add something before someone falls putting a board away. I have heard that once it touches, it is there to stay.

Alot of scraping and thinner will get it off, it just sucks. Also depends what material it is and how it was put on. If it was pressure-sensitive (peel & stick) you will have better luck. If it was old hydroturf and they used contact cement you will never get it "clean". Although I've put new Hydroturf on top of cleaned and scraped contact cement with good results.